A typical semiconductor fabrication facility includes a plurality of processing systems (“tools”) in which a sequence of process steps is performed on a workpiece (a silicon substrate, a glass plate, etc.). These steps may include polishing, deposition, etching, photolithography, heat treatment, and so forth. In general, these processes are performed at various locations within the fabrication facility, and it is accordingly necessary that substrates be transported within the facility from one processing location to another.
It is conventional to transport substrates from one processing location to another within substrate carriers such as sealed pods, cassettes, containers and so forth. It is also conventional to employ automated substrate carrier transport devices, such as automatic guided vehicles, overhead transport systems, substrate carrier handling robots, etc., to move substrate carriers from location to location within the fabrication facility or to transfer substrate carriers from or to a substrate carrier transport device.
In a typical automated substrate handling system, a substrate carrier is transported to a loadport where an end effector (e.g., of a robotic arm) may load substrates into or remove substrates from the carrier. A conventional loadport must open the carrier door in order to sense the presence of a substrate in the carrier. Opening a carrier door takes time, and also potentially exposes the interior of the carrier to contaminants. Accordingly, it is desirable to have methods and apparatus for sensing the presence of a substrate in a carrier at a loadport without the need for opening the carrier door.